Method and system for de-jittering of transmitted MPEG-2 and MPEG-4 video

Abstract

The present invention relates to an improved method of de-jittering MPEG-2 and MPEG-4 data that is transmitted over a network. First, a network system jitter associated with periodic reference data packets is estimated. Then, the estimated system jitter is used to adjust clock-stamped reference values in the data packets before they are provided to the PLL for clock synchronization. The invented de-jittering method improves the PLL's ability to synchronize the MPEG data and provides for a better quality playback.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority under 35 U.S.C. § 119 based on U.S. Provisional Application Ser. No. 60 / 167,339, filed Nov. 24, 1999, the disclosure of which is incorporated by reference.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]This invention was made with Government support under Contract No. DAAL-01-96-2-0002, awarded by the U.S. Army Research Laboratory. The Government has certain rights in this invention.FIELD OF INVENTION[0003]This invention relates generally to the field of multimedia transmission over a network. More specifically, this invention relates to method of de-jittering MPEG-2 and MPEG-4 video data transmitted over a packet switched network.BACKGROUND OF THE INVENTION[0004]The MPEG-2 and MPEG-4 standards are well-known in the art for coding and storing multimedia video and associated audio information. When MPEG multimedia data is transmitted over a network from a source device to a destination...

AI Technical Summary

Benefits of technology

[0007]The present invention comprises an improved method and system for reducing jitter in MPEG data transmissions due to non-constant network delay times. Generally, the present invention calculates a statistical estimation of the average network system jitter. The estimated average network system jitter is then used to re-calculate a “corrected” reference value for subsequent clock-stamp reference values. Specifically, for each data packet that contains a clock-stamp reference value, the clock-stamp reference value is parsed out from the rest of the data packet. The average network jitter is estimated based on a prior predetermined sample of data packets. An estimated jitter is then calculated for the reference data packet. The estimated reference jitter is then translated to clock tics and a “corrected” clock-stamp reference value is calculated. Finally, the original clock-stamp reference value of the subsequent reference data packet is replaced with the “corrected” clock reference value, which includes compensation for the statistical estimation of network jitter, before it is sent to a phase locked loop (PLL). Since the new clock reference values are “corrected” based upon the statistical estimation of the average network system jitter, the phase error of the PLL is minimized, resulting in a more stable system time clock (STC). Among other benefits, the present invention improves the quality of the received video and enables the system to tolerate more network jitter without video degradation.

Problems solved by technology

However, it is difficult, if not impossible, to maintain a constant network delay.

Non-constant network delays, known as “jitter”, can result in a degradation of the video playback.

Jitter results in data packets arriving at the destination device in a non-uniform manner, which impedes effective clock synchronization by the PLL.

This, in turn, slows down the responsiveness of the PLL and affects the maximum phase error introduced by the PLL between the clock-stamped reference values encoded from the source device's clock and the corresponding destination device's time clock references.

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